To Prove One's Self
by Revamped Persona
Summary: After the events of the first Devil Survivor game, the Black Frost known as Frosty returned to the world he originated from. However a familiar belt shatters his now peaceful lifestyle, as he is forced to carry the mantle of Kamen Rider Decade. Can an actual demon prove himself to be the hero he yearns to be, or will he destroy everything he cares for due to his chaotic nature?


**AN: Thanks for reading my new fanfic! I hope that you enjoy it!  
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 _In the depths of an ice covered world…_

A small black creature was seen wandering about. It had red eyes and a large toothy grin on its face. It wore a violet hat with jagged "ears" on the sides and had a small yellow logo in the center. It's small black body was as cold as ice. It walked around on purple boots with pointed ends and yellow cuffs. Completing the look, was a spiky purple scarf.

"Hee ho!" The creature yelled as it spun around, "I'm the protector of love and justice, Black Frost!"

Black Frost is a demon from the "demon world". His kind were born if a Jack Frost, the more recognizable version of his species remembered their true purpose as a demon, yet this specific Black Frost felt no intent to do wicked things. Instead he only felt the need to punish the wicked and save the defenseless. Although the one who taught him to love, Midori was unreachable, he still carried on, promising to himself that he'll see her again. The snowman didn't know how, but he knew it in his heart that he'll one day see her again. The only person he could truly call "friend" and the one who gave him the nickname "Frosty".

The demon didn't know exactly when he would see her since their two world's timelines are different, but he does sometimes dream of places other than the deserted wasteland he now resides in. Sometimes he's in a large tower, or drifting in a lab, he even once saw a large place that humans call a "casino". The one thing in common is that he always assisted the humans that needed his help. Frosty supposed that even in his sleep, he couldn't help but aid others. However… today just felt… different.

It wasn't the atmosphere, the landscape, or even himself. Frosty just knew that something was different.

"Why…?" He questioned, adjusting his hat. "Why do I feel something strange hee ho?" Of course the feeling wouldn't simply go away. He tried ignoring it, but the tingling sensation he felt wouldn't stop.

With no other option, the Black Frost moved to where he felt the feeling the strongest. Frosty didn't quite understand what it could be. He knew that there shouldn't be anymore problems in Midori's world, he made sure of that. He also knew that the other groups of humans saved their respective worlds too, so why did he feel so uneasy and on edge?

And then he saw the belt.

It wasn't too big, and looked like it could fit him, yet it was the strangest belt Frosty had ever seen. The belt was mainly black, white, and gray. The middle was large and had three round lights on each side as well as a giant one on the middle. The strangest part was the slot on top of it that looked as if you could insert something into it and the symbols all around the middle.

"What the hee ho hell is this?" Frosty asked, yet he knew he wouldn't get a response. He was alone after all. "I've seen belts before in the human world, but never one like this."

As he got closer, he noticed something else. Picking it up, Frosty spotted that it was a strange card with a picture of a helmeted figure with green bug shaped eyes. The suit was what he thought was hot pink and the card had " _Decade_ " written on it.

"Decade…" The protector of love and justice mumbled. "Decade, Decade, Decade… where have I heard that name before…?" And then he _remembered_.

There was a show that he remembered watching during his brief time in the human world about a fellow protector of justice, _Kamen Rider_ Decade. He wasn't sure why it was here, but he recognized it as the object that the hero used to transform with.

Before he could think of what to do with the objects, he felt the tingling feeling return to him at full force. Frosty fell down to his knees as the world seem to turn gray. "No no no no no!" Frosty panicked as he tried to use his null magic on himself to stop the feeling, but it wouldn't halt. "I can't go out like this hee ho!" he wailed, "I'm a protector of love and justice!" And he felt a tugging sensation in his stomach, as he tumbled backwards into a ripple in space.

As the Black Frost was sent away, a man could be seen watching from the distance. His most distinguishing features include a tan coat, hat, and the glasses perched on his nose.

"So another devil threatens to destroy every world he touches…" The man muttered, his eyes showing nothing but pure hatred at the thought of _him_.

"Damn you Decade…"

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"Heeeeeeeee Hoooooooooo!" Frosty screamed as he fell for what felt like decades. He didn't know why he was sucked into this mess, but he can't escape now. As he kept falling, he didn't notice that the belt ejected a small square holster and the Decade card moving inside of it.

Finally he was spat out and roughly landed on the hard ground. It was incredibly painful, but Frosty knew that he would survive. He's dealt with worse after all.

"Where… am I?" He questioned, looking around. It was a place he was unfamiliar with. The houses looked older with orange rooftops, the sky has a purplish orange hue, and a large castle can be seen overhead. Frosty knew that this wasn't home, but it wasn't the human world either. The only clue he had was the belt.

"What the hell is this thing?!" Frosty shouted, frustrated at the fact he was forced out of his home and is now stuck in a place he had no knowledge about because of the belt. At least if it were the human world he could attempt to contact Midori. He had no such luck in this place.

Speaking of the belt, it was now stuck on his waist with a new square shaped hollister on the side that he recognized as the Ride Booker. Frosty unclipped it and opened it to see more cards featuring nine other Riders, attack cards, form ride cards, and the final attack ride cards. Frosty tried removing the belt after putting the Ride Booker back on the side, but it wouldn't budge. Everytime the snowman tried, it would beep and tighten its grip around him.

"Shit…" He grumbled, finally giving up attempting to remove it. Frosty would have to try later. Instead he began to walk in an aimless direction, not knowing the layout of the land. Nothing about this place was familiar to him at all. As he kept wandering down the road, he noticed that no one was giving him any looks. It was as if the inhabitants were already used to seeing people like him.

Finally, he stumbled onto a strange sight. In the center of a market stood what he thought was a demon, but it was completely gray with red eyes. It bore a faint resemblance to a polar bear, but it had crimson eyes and held a mace. As it attacked the humans fleeing in terror, it laughed maniacally and kept yelling, "Tremble before the might of NEO SHOCKER!"

Frosty didn't know what was going on, but he knew that he had to stop this before someone dies. Without thinking, he sprung over and shot a low powered Mudo at the Shirokuma Orphnoch to get its attention. "Hey fatso!" He called out, "Why not try killing something more worthwhile like me hee ho?"

The bear turned around pissed off at the small demon who dared to attack him, one of the generals of the Neo SHOCKER Army. However that all changed when he laid eyes on the Driver that the dimension traveling menace wore now on the Black Frost's waist.

" _Decade_ …" It hissed, glaring at the snowman.

"What?"

"DECADE! You'll pay for your intrusion with your life!" The Orphnoch howled, not giving the Frost a chance to speak. The Shirokuma Orphnoch pounced straight at him, mace at the ready to kill. Frosty barely had enough time to move out of the way before it was too late. He tried using every spell he knew. Mabufu, Bufudyne, and even Mudoon couldn't even give the polar bear a scratch. Frosty panicked, not knowing what to do until he remembered the belt around his waist.

"Please work…" Frosty prayed as he took the Decade card out of the Ride Booker preparing to use it for the very first time. As he was doing so, the Orphnoch noticed what he was about to do and once again started to rush towards him.

Just like in the show, the belt's buckle opened revealing the place to insert the card he held tightly.

 **KAMEN RIDE**

Frosty didn't hesitate slotting in the card in his hand, shouting with all his might as the buckle closed with the chosen card inside.

"HENSHIN"

 **DECADE**

Silvery silhouettes of other Kamen Riders appeared around him, combining into one figure. He was noticeably taller than the Black Frost he previously was, having a hot pink color scheme. A black and white criss cross symbol was on the upper right side of his chest. The belt ejected some black card like objects that embed themselves onto the helmet. A small gold square added the final touch, giving the whole suit color. The bug like eyes were a bright shade of green and on his waist was the Decadriver used to transform in the first place.

"What the…" Decade muttered, placing a hand on his helmet. He couldn't believe what had happened to him. Frosty, Defender of Love and Justice had transformed into a Kamen Rider. He was sure that not even a demon like him was capable of even doing that, yet here he was.

However before he could carefully look at himself, the Shirokuma Orphnoch attempted to strike him in the face. Decade lepted out of the way and sent a roundhouse kick at the polar bear slamming him against a wall.

*BAM*

The Orphnoch howled in pain as it felt a staggering blow as Decade quickly took out the cards he had. Frosty faintly remembered how they worked, but he hasn't seen the show in years. He pulled out one of the Attack Cards and hoped it would be enough.

 **ATTACK RIDE: SLASH!**

The Ride Booker turned into a sword as Decade quickly swung it just as the Shirokuma Orphnoch tried to stab him with one of its claws. The sword made quick work of it and the bear's right arm fall off and turned to ash.

"Grr… how dare you strike at me?!" It sneered, its red gaze showing no hint of the hunity it once had. "I oughta turn you into a bunch of holes!" The Shirokuma Orphnoch tried one last ditch effort to kill Decade using its left arm to swing the mace at him. Frosty only had one response to this.

 **FINAL ATTACK RIDE: D-D-D-DECADE!**

Decade leapt up into the air as a line of translucent cards before him formed into a line. He then started his diagonal descent downwards towards the reckless Orphnoch running straight towards him. The more cards he kicked into, the stronger and faster the attack became. Finally the attack made contact, striking the Shirokuma Orphnoch's chest with the force of a freight train. "Don't… underestimate… the power… of Neo SHOCKER…!" The polar bear wheezed as it finally exploded.

*BOOM*

The explosion was loud, yet it was less exaggerated than in the show. It was a fairly small explosion compared to the hell that Frosty witnessed in Tokyo. Decade took out the card, and returned to his more mischievous appearance. The Frost was nearly out of breath. The transformation took a lot out of him and he felt like he was going to pass out at any moment. Just as he was about to let go, he heard a soft voice from behind him.

"Are you okay?"

Before he could respond, Frosty felt himself black out, his body resting after a harsh day.

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 **AN: So here is an interesting concept for a crossover… a demon from Shin Megami Tensei being given the duty of a Kamen Rider. Frosty is the first of his kind, yet what happened to Tsukasa? What is Neo SHOCKER planning? Where is he? And who was the stranger talking to him?**

 **Find out next time in Chapter 2!**


End file.
